1. Field of the Invention
The present invention relates to a dose setting limiter for medical injectors of the type having a housing accommodating an ampoule containing medicine sufficient for a number of dosed injections, a rotary dose setting knob, which is rotational relative to the housing and by which doses may be set by rotating the dose setting knob and an injection button which, when pressed, administers the set dose.
2. Description of the Related Art
Commercially accessible medical injectors of the above-mentioned type are normally capable of being set to dispense a wide range of doses. Some medication, such as insulin, is often self-administered. The typical diabetes patients will require injections of insulin several times during the course of the day. Normally the size of the doses is prescribed and the dose setting knob of the injection device is therefore always rotated to the same amount before each injection. Due to this there is a great need for an auxiliary dose setting limiter, which can be applied to a medical injector, and which can help setting up the exact same dose every time.
An auxiliary dose setting limiter of this kind is known from WO 99/64092. This dose setting limiter is cup-shaped and is placed retentively over the dose setting knob in a position where a projection on the dose setting limiter aligns the desired dose. When in use, the injection dose is first being set by rotating the dose setting knob, which knob can only be rotated until the pre-set dose is reached, while the projection on the dose setting limiter will be arrested by a stationary raised stud on the injection pen. This known dose setting limiter can only be applied to a traditional pencil-shaped injection device of the type having the dose setting knob placed at the rear end of the pen and a stationary raised stud indicating the zero mark of the scale.
It is an object of the invention to provide a dose setting limiter, which can be fitted on to a large variety of injection devices. It is a particular object to provide a dose setting limiter that can be fitted on to the new generation of very short injection devices e.g. known from U.S. Pat. No. 5,947,934.
This is obtained by a dose setting limiter for medical injectors of the type having a housing accommodating an ampoule containing medicine sufficient for a number of dosed injections, a rotary dose setting knob, which is rotational relative to said housing and by which doses may be set by rotating said dose setting knob and an injection button which, when activated, administers the set dose, said dose setting limiter comprising:
a stationary first part connected to said housing, and
a second part fitted over said rotary dose setting knob, said second part being able to rotate together with said dose setting knob when setting up a dose and said second part being rotational relatively to said first part,
which dose setting limiter according to the invention has a third part placed between said first part and said second part, said third part having means cooperating with means on said second part for limiting the dose setting.
The desired dose is first set by rotating the third part with the auxiliary dose setting limiter disconnected from the injection device. When the marker on the third part is positioned in alignment with the desired dose indicated on the scale and the dose setting limiter is fitted on to the injection device, the position of the protrusion on the third part is locked relatively to the shell, due to the friction between the two parts. When setting up a dose by rotating the dose setting dial, the protrusion on the dose setting dial will be arrested by the protrusion on the third part when the predetermined dose is being reached.
The third part need not be loose and rotational, but could be permanently fastened to the shell. The permanent location of the protrusion on the third part would then be the maximal dose, which could be dialed up when the particular shell is connected to the injection device. Different dose setting limiters each having a different maximal dose setting could be made available for the consumer. This would present a very attractive solution for parents wanting to set a maximal dose on the injection device for a child.
In one embodiment of the dose setting limiter according to the invention the third part can move freely when the first part is disconnected from the housing of the injection device, but is locked to the first part when the first part is connected to said housing. The locking is usually done by friction between the injection device, but the ring and the shell could also be preformed by a tooth gearing between the shell and the ring, the ring e.g. having pawls being arrested in depressions in the shell, or by other adequate means arresting the ring when the shell is being connected to the injection device.
The locking is, according to another embodiment of the dose setting limiter, done by a number of holes in the third part being arrested by a number of raised studs on the inside surface of the first part. With the shell being disconnected from the injection device, the user is provided with a clicking feeling, and a click sound, when the ring is rotated relative to the shell, due to the engagement between the holes in the ring and the raised studs on the shell.
In a preferred embodiment of the dose setting limiter according to the invention the means located on the second part and the means on the third part are protrusions. Protrusions are easily manufactured and abut one another in a useful manner.
The third part is, according to yet another embodiment of the dose setting limiter, a flat circular ring fitted inside the first part and the protrusion protrudes inwardly pointing towards the center of the circular ring. By making the third part as a flat ring the thickness of the dose setting limiter can be kept very little. Due to this the total size of the injection device is almost unchanged when the auxiliary dose setting limiter is connected to the injection device.
In a fifth embodiment of the dose setting limiter according to the invention the second part, forming a dose setting dial, is circular and rotational connected to the first part and has the protrusion protruding outwardly. By making the dose setting dial circular it fits onto a large variety of injection devices, while such devices traditionally have a circular dose setting knob.
In yet another embodiment of the dose setting limiter according to the invention the first part, forming a shell, is circular and has a plurality of flanges that fit retentively around said housing, thereby locking said shell to said housing. The shell can be made to fit very tightly to the injection device, making it almost impossible for people with only limited physical strength to remove the dose setting limiter. In that way parental setting of a predetermined dose is irreversible for a child.
In a further embodiment of the dose setting limiter according to the invention the shell has an area on the circular periphery cut off, making the ring accessible for rotation relative to the shell. This allows the user to get a good grip with the fingers on the ring when setting up a dose.
In yet a different embodiment of the dose setting limiter according to the invention the shell is transparent and the ring has a marker visible through the shell, which marker indicates the location of the protrusion on the ring. Since the marker is visible through the transparent shell the preset dose can easily be read on the scale of the shell.
According to the last embodiment of the dose setting limiter according to the invention the dose setting dial can only be rotated until the protrusion on the dose setting dial is arrested by the protrusion on said ring. With the ring being locked onto the shell it is impossible to rotate the dose setting dial beyond the predetermined dose.